The invention pertains to semiconductor processing and in particular, to an improved atomic layer deposition method and system using a point of use generated reactive gas species for semiconductor processing.
Atomic layer deposition (ALD), also known as atomic layer epitaxy (ALE) and atomic layer chemical vapor deposition (ALCVD), offers many advantages over the traditional deposition methods. ALD relies on self-limiting surface reactions in order to provide accurate thickness control, excellent conformality, and uniformity over large areas. As the microscopic features on a chip grow increasingly narrow and deep, these unique features make ALD one of the most promising deposition methods in the manufacturing of the future circuits.
The feature that makes ALD a unique deposition method compared to chemical vapor deposition (CVD) is that it deposits atoms or molecules on a wafer a single layer at a time. Additionally, ALD films are deposited at temperatures significantly lower than comparable CVD processes, thereby contributing to lower thermal exposure of the wafer during processing. Furthermore, as another distinction from CVD methods, no strict precursor flux homogeneity is required in ALD because of the self-limiting growth mechanism. The flux has only to be large enough to fully saturate the surface with the given reactant. This enables, for example, the utilization of low vapor pressure solids, which are difficult to be delivered at constant rates.
ALD accomplishes deposition by introducing gaseous precursors alternately onto a workpiece such as, for example, semiconductor substrate or wafer. Under properly adjusted processing conditions, i.e., deposition temperature, reactant dose, length of precursor, and purge pulses, a chemisorbed monolayer of a first reactant is left on the surface of the workpiece after a purge sequence. Typically, the purge sequence is completed by evacuating or purging the entire reactor chamber. Afterwards, the first reactant is reacted subsequently with a second reactant pulse, such as a flux of a generated reactive gas species, to form a monolayer of a desired material along with any gaseous reaction byproducts, such as when compounds are used as precursors. The surface reactions are self-controlled and produce no detrimental gas phase reactions, thereby enabling accurate control of film thickness by counting the number of deposition cycles.
In one particular ALD method, there is a high degree of interest in using a point of use generated reactive gas species. However, for ALD processes, it is difficult to generate a high flux of short-lived reactive gas species on the surface of the wafers and cycle it through a number of on/off states at a fast rate required for high throughput ALD processes.
The present invention solves the above-mentioned difficulties by providing an improved atomic layer deposition method and system. In particular, a dispenser unit according to the present invention is used with a point of use generated reactive gas species for atomic layer deposition, which permits the cycling of the system through a number of on/off states at a fast rate for higher processing throughput.
In a reaction chamber containing a workpiece, a precursor gas is flown directly onto an exposed surface of the workpiece from the dispenser unit to form a surface reactant thereon. Additionally, an input gas is flown in through a side of the dispenser unit. The flows of precursor and input gases are separated by a pump/purge setup on the dispenser unit designed to prevent mixing. As the workpiece is scanned under the dispenser unit to form the surface reactant, the input gas is exposed to a focused beam of electromagnetic radiation. The electromagnetic radiation dissociates a gaseous constituent of the input gas creating the high flux of point of use generated reactive gas species. The incoming flux of the generated reactive gas species reacts with the surface reactant in a complete and self-limiting reaction forming a desired monolayer of a material thereon. Multiple dispenser units can be used to increase the ALD process.
A system and apparatus for generating a high flux of short-lived activated reactive gas species using transmission gas (es) is disclosed by commonly assigned patent application: Ser. No. 09/998073 for xe2x80x9cA Method to Provide High Flux of Point of Use Activated Reactive Species for Semiconductor Processing,xe2x80x9d filed on Nov. 30, 2001, which is herein incorporated fully by reference.
In one aspect, the present invention encompasses a method of chemically treating a surface of a workpiece. The method comprises exposing the surface of the workpiece to a direct flow of a precursor gas to form a surface reactant thereon, and providing a flow of an input gas above the surface of the workpiece. The method further comprises preventing the mixture of the precursor gas and the input gas with a purge gas, directing a beam of electromagnetic radiation into the input gas to produce a high flux of generated reactive gas species, and reacting the generated reactive gas species with the surface reactant.
In another aspect, the present invention encompasses a system for chemically treating a surface of a workpiece. The system comprises a supply of an input gas, a supply of a precursor gas, and a supply of a purge gas. A dispenser unit is adapted to expose the surface of the workpiece to a direct flow of the precursor gas for a surface reactant formation, to provide a flow of the input over the workpiece, and to provide the purge gas between the precursor gas and the input gas to prevent mixing of the precursor and input gases. The dispenser unit further includes a pair of evacuation ports for evacuating the purge gas. A source is adapted to converge a beam of electromagnetic radiation in the flow of the input gas in close proximity to the surface of the workpiece, but spaced a finite distance therefrom, to dissociate the input gas into a high flux of generated reactive gas species that reacts with the surface reactant to chemically treat the surface of the workpiece.
In still another aspect, the present invention encompasses a dispenser unit adapted for use in a reaction chamber for atomic layer deposition of a material onto a surface of a workpiece. The dispenser unit comprises a first gas port adapted to provide a flow on an input gas over the surface of the workpiece to be dissociated by a radiation beam into a point of use generated reactive species. Further included is a second gas port adapted to provide a direct flow of a precursor gas onto the surface of the workpiece which by chemisorption forms a first surface reactant, and a third gas port adapted to flow a purge gas to prevent mixing of the input and precursor gases. Also provided is a pair of evacuation ports adapted to evacuation at least the purge gas.
These and other features and objects of the present invention will be apparent in light of the description of the invention embodied herein.